The study was performed in susceptible to poliovirus (PVR) transgenic mice developed by A. Nomoto and his colleagues (Koike, et al., 1991). Continuing this project in 1994 we found that intraspinal (IS) inoculation of another, PVR Tg21 mouse line proved to be the appropriate system for type 3 oral poliovirus vaccine neurovirulence in its correlation with the monkey test: it was able to distinguish vaccine lots which passed and filed the monkey test. We demonstrated also that PVR Tg1 mice, inoculated IC with type 1 polioviruses, were able to discriminate not only between a wild-type strain, Sabin vaccine revertants and original vaccine virus, but even between Sabin vaccines which passed and failed the monkey test. Moreover, the mouse system identified those vaccine preparations which contain increased percentage of back-mutations at position 480 (G->A) and 525 (U->C) of the genome and sometimes passed while other times failed the monkey test (~borderline~ samples). The project will be continued. A paper is in progress. The data were reported at the US-Japan Meeting on the Development of the Poliovirus Receptor Transgenic Mice as a Laboratory Animals in March 1994.